| 1. |
- Andõn, F. T., et al.
(författare)
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Biodegradation of Single-Walled Carbon Nanotubes by Eosinophil Peroxidase
- 2013
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Ingår i: Small. - : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 9:16, s. 2721-2729
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Tidskriftsartikel (refereegranskat)abstract
- Eosinophil peroxidase (EPO) is one of the major oxidant-producing enzymes during inflammatory states in the human lung. The degradation of single-walled carbon nanotubes (SWCNTs) upon incubation with human EPO and H2O 2 is reported. Biodegradation of SWCNTs is higher in the presence of NaBr, but neither EPO alone nor H2O2 alone caused the degradation of nanotubes. Molecular modeling reveals two binding sites for SWCNTs on EPO, one located at the proximal side (same side as the catalytic site) and the other on the distal side of EPO. The oxidized groups on SWCNTs in both cases are stabilized by electrostatic interactions with positively charged residues. Biodegradation of SWCNTs can also be executed in an ex vivo culture system using primary murine eosinophils stimulated to undergo degranulation. Biodegradation is proven by a range of methods including transmission electron microscopy, UV-visible-NIR spectroscopy, Raman spectroscopy, and confocal Raman imaging. Thus, human EPO (in vitro) and ex vivo activated eosinophils mediate biodegradation of SWCNTs: an observation that is relevant to pulmonary responses to these materials. Human eosinophil peroxidase (EPO) is able to degrade SWCNTs in vitro in the presence of H2O2. EPO is one of the major oxidant-generating enzymes present in human lungs during inflammatory states. The biodegradation of SWCNTs is evidenced also in an ex vivo culture system using primary murine eosinophils stimulated to undergo degranulation. These results are relevant to potential respiratory exposure to carbon nanotubes.
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| 2. |
- Pushp, Mohit, et al.
(författare)
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Ageing tests closer to real service conditions using hyper-sensitive microcalorimetry, a case study on EPDM rubber
- 2023
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Ingår i: Polymer testing. - : Elsevier Ltd. - 0142-9418 .- 1873-2348. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- Accelerated thermal ageing (ATA) coupled to mechanical testing is widely used to predict the lifetime of polymeric products. ATA implies that the mechanisms of ageing are the same at accelerated and service conditions, which may often not be the case. Hence, ageing closer to service conditions is of high importance, but require very sensitive tools. Therefore, a high sensitivity microcalorimetry (MC) method was applied here to assess if it can be a possible tool for lifetime/ageing prediction closer to service conditions. We chose to focus on a complex, yet commonly used, ethylene-propylene-diene terpolymer (EPDM) rubber. Arrhenius extrapolation of the heat flow data indicated two regimes at low and high temperature, with the former having the lower activation energy. The heat flow values measured by the MC revealed contributions from processes such as the melting of the antioxidant, its consumption at low temperature and the breakdown of residual peroxide. MC tests on the EPDM indicated a very low degree of oxidation appearing above 100 °C, too low to be observed with infra-red spectroscopy (FTIR), but noticeable with MC. The high sensitivity of the MC techniques enabled detection of early signs of polymer degradation/ageing and other thermally activated processes that take place at or close to service temperatures (such as those in nuclear power plants). The MC tests were combined with other techniques, such as scanning electron microscopy/energy dispersive X-ray spectroscopy, gas chromatography techniques, differential scanning calorimetry and FTIR to further understand the degradation mechanisms. © 2023 The Authors
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| 3. |
- Wei, Xin-Feng, et al.
(författare)
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Microplastics generated from a biodegradable plastic in freshwater and seawater
- 2021
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- Biodegradable polymers have been regarded as a promising solution to tackle the pollutions caused by the wide use of conventional polymers. However, during the biodegradation process, the material fragmentation leads to microplastics. In this work, the formation of microplastics from biodegradable poly (butylene adipate-co-terephthalate) (PBAT) in different aquatic environments was investigated and compared with the common non-biodegradable low-density polyethylene (LDPE). The results showed that a much larger quantity of plastic fragments/particles were formed in all aquatic environments from PBAT than from LDPE. In addition, UV-A pretreatment, simulating the exposure to sunlight, increased the rate of PBAT microplastic formation significantly. The size distribution and shapes of the formed microplastics were systematically studied, along with changes in the polymer physicochemical properties such as molecular weight, thermal stability, crystallinity, and mechanical properties, to reveal the formation process of microplastics. This study shows that the microplastic risk from biodegradable polymers is high and needs to be further evaluated with regards to longer timeframes, the biological fate of intermediate products, and final products in freshwater, estuarine and seawater natural habitats. Especially, considering that these microplastics may have good biodegradability in warmer 20 & ndash; 25 degrees water but will most likely be highly persistent in the world & rsquo;s cold deep seas.
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| 4. |
- Wei, Xin-Feng, et al.
(författare)
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Microplastics Originating from Polymer Blends : An Emerging Threat?
- 2021
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55:8, s. 4190-4193
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Tidskriftsartikel (refereegranskat)abstract
- No one can have missed the growing global environmental problems with plastics ending up as microplastics in food, water, and soil, and the associated effects on nature, wildlife, and humans. A hitherto not specifically investigated source of microplastics is polymer blends. A 1 g polymer blend can contain millions to billions of micrometer-sized species of the dispersed phase and therefore aging-induced fragmentation of the polymer blends can lead to the release of an enormous amount of microplastics. Especially if the stability of the dispersed material is higher than that of the surrounding matrix, the risk of microplastic migration is notable, for instance, if the matrix material is biodegradable and the dispersed material is not. The release can also be much faster if the matrix polymer is biodegradable. The purpose of writing this feature article is to arise public and academic attention to the large microplastic risk from polymer blends during their development, production, use, and waste handling.
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| 5. |
- Wei, Xin-Feng, et al.
(författare)
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Risk for the release of an enormous amount of nanoplastics and microplastics from partially biodegradable polymer blends
- 2022
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 24:22, s. 8742-8750
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Tidskriftsartikel (refereegranskat)abstract
- Nanoplastics and microplastics (NMPs) in natural environments are an emerging global concern and understanding their formation processes from macro-plastic items during degradation/weathering is critical for predicting their quantities and impacts in different ecological systems. Here, we show the risk of enormous emissions of NMPs from polymer blends, a source that has not been specifically studied, by taking immiscible (most common case) partially biodegradable polymer blends as an example. The blends have the common “sea-island” morphology, where the minor non-biodegradable polymer phase (polyethylene and polypropylene) is dispersed as NMP particles in the major continuous biodegradable matrix (poly(ϵ-caprolactone)). The dispersed NMP particles with spherical and rod-like shapes are gradually liberated and released to the surrounding aquatic environment during the biodegradation of the matrix polymer. Strikingly, the number of released NMPs from the blend is very high. The blend film surface erosion process, induced by enzymatic hydrolysis of the matrix, involving fragmentation, hole formation, and hole wall detachment, was systematically investigated to reveal the NMP release process. Our findings present direct evidence and detailed insights into the high risk of emissions of NMPs from partially biodegradable immiscible polymer blends with a widespread “sea-island” morphology. Efforts from authorities, developers, manufacturers, and the public are needed to avoid the use of non-biodegradable polymers in blends with biodegradable polymers.
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| 6. |
- Wei, Xin-Feng, et al.
(författare)
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Visualizing undyed microplastic particles and fibers with plasmon-enhanced fluorescence
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier B.V.. - 1385-8947 .- 1873-3212. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- Despite widespread awareness that enormous consumption of plastics is not sustainable, the global production and use of plastics continue to grow. This generates vast amounts of plastic waste and microplastics, ending up e.g., in the marine environment. There are serious challenges in detecting and measuring microplastics, especially in highly diluted natural samples. Here, a new alternative microplastic detection method based on plasmon-enhanced fluorescence (PEF) was developed and tested using fluorescence microscopy. In particular, gold nanopillar-based substrates, displaying (i) high electromagnetic field enhancement, and (ii) surface superhydrophobicity and high adhesion properties, were utilized to enhance the fluorescence emission signal from microplastics in water samples. The fluorescence microscopy imaging revealed remarkable fluorescence enhancement by the PEF substrates on the microplastic particles and fibers with different sizes of both conventional, low-density polyethylene, and biodegradable poly (butylene adipate-co-terephthalate). The limit of detection and quantification by this method was estimated to be as low as 0.35 and 1.2 femtograms, respectively. The observed fluorescence enhancement of the gold nanopillar substrates for the microplastics was ca. 70 times greater than the case of having the microplastics on a glass substrate. Additionally, 3D FEM simulations were performed to further investigate the system's electromagnetic field distribution near the nanostructures. This new method makes undyed microplastics visible in fluorescence microscopy, even particles and fibres too small to be imaged with conventional light microscopy. This can be a great tool for microplastic research, helping us to detect, study, understand microplastic dynamics in water based systems. © 2022 The Authors
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| 7. |
- Ye, Xinchen, et al.
(författare)
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Protein/Protein Nanocomposite Based on Whey Protein Nanofibrils in a Whey Protein Matrix
- 2018
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 6:4, s. 5462-5469
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Tidskriftsartikel (refereegranskat)abstract
- This article describes nanocomposite films with separately grown protein nanofibrils (PNFs) in a nonfibrillar protein matrix from the same protein starting material (whey). Tensile tests on the glycerol-plasticized films indicate an increased elastic modulus and a decreased extensibility with increasing content of PNFs, although the films are still ductile at the maximum PNF content (15 wt %). Infrared spectroscopy confirms that the strongly hydrogen-bonded beta-sheets in the PNFs are retained in the composites. The films appear with a PNF-induced undulated upper surface. It is shown that micrometer-scale spatial variations in the glycerol distribution are not the cause of these undulations. Instead, the undulations seem to be a feature of the PNF material itself. It was also shown that, apart from plasticizing the protein film, the presence of glycerol seemed to favor to some extent exfoliation of stacked beta-sheets in the proteins, as revealed by X-ray diffraction.
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